Aluminum-magnesium alloys



Patented May 3, 1932 UNITED srArss PATENT OFFICE- ROBERT S. ARCHER, OF LAKEWOOD, AND LOUIS W. KEMPF, CLEVELAND, OHIO ALUMINUM-MAGNESIUM armors 1T0 Drawing. Application filed May 21,

garde because of the-well known diificulties encountered in attempting to cast or fabri- Hi cate them. Moreover, it as been generally thought that such alloys do not possess hyslcal properties of sufiicient magnitude to Justify their use as replacements for the excellent high strength aluminum alloys already in extensive commercial use. Recentl however, improvements in the alloys themselves and in methods of handling them, for example methods of casting and heat treating aluminum alloys containing between about 5 and 16 per cent and even up to about 20 er cent, of magnesium have greatly exten ed the field of utility of these alloys in both cast and fabricated form. With these improvements the alloys are comparable to other aluminum base alloys in physical properties, with the additional advantage of light wel 'fiie object of the present invention is to improve aluminum-magnesium alloys still further in the direction of the physical properties which largely affect their usefulness. Heretofore in the art it has been the belief that the addition of a third ingredient to a binary alloy may improve the alloy in one respect orv another but that the addition in many cases impairs the alloy 1n some other respects. For example, the addltlon of small amounts of magneslum to binary alloys of aluminum and sllicon increases the tensile strength but decreases the elongation. We

1930. Serial No. 454,510.

have found, however, that the e stated is not true for certain additions f man anese to aluminum-magnesium alloys, and t at by the addition of small amounts of manganese an lmprovement can be obtained in some of u the physical properties without material impairment of others.

The aluminum-magnesium alloys in which these results may be produced by the addition of manganese are those containing substantial amounts of magnesium, say between about 5 and 16 per cent, and in general it is within this range that the most useful alloys of this nature occur. Alloys containin from about 5 to 12 per cent have been foun to possess the best properties under most conditions and alloys containing about 10 er cent of magnesium are particularly usefu The amount of manganese which may be added to obtain the desired improvements 5 varies over a comparatively narrow range. Our experience indicates that the addition of much more than 3 per cent has the effect of" embrittling the alloys and making them difficult to cast. Below about 3 per cent the manganese produces a favorable increase in properties even when added in amounts as low as 0.1 per cent, but for the best results the preferred addition ranges from about 0.2 to 1.5 per cent. For example, a forging of an alloy containin 6 per cent of magnesium and 1.25 per cent oi manganese, without heattreatment, showed a tensile strength of about 56,000 pounds per square inch and a degree of ductility indicated by an elongation of about 23 per cent in two inches.

The alloys may be com ounded in the molten state by well known a loying methods. For instance, the aluminum-magnesium al- 10y may be made by melting the aluminum as and then adding the magnesium to the molten aluminum. The-manganese may then be introduced by adding the proper amount of an aluminum-manganese alloy containing about 10 per cent of manganese.

Aluminum-magnesium alloys containing small amounts of manganese are amenable-to fabricatin processes, suchas rolling, extrusion, forging and the like; and in all cases the addition of manganese defimtely 1ncreases the physical properties of the alloy. Also in extruded form aluminum-magnesmrn alloys containing manganese possess combinations of physical properties seldom reached or excelled in other extruded aluminum al-- purities, mostly silicon and iron.

Table N 0. 1

Yield Tensile Elonga- Per cent Per cent point stmn h tion Brinell 3% of g: lbs. lbs. r cent Bi hardness sq. sq. inches A 10 28. mo 56, 900 24 to 30 93. 1 B 10 0. 5 30,840 65,220 31. 7 101. 2 C 10 24.210 65.880 -37. 7 86.9 D 10 0. 5 28, 800 63, 650 36 95. 1

In Table No. 2 is illustrated the efi'ect of adding increased amounts of manganese to those alloys. E,-F and G represent the alloys in the as extruded condition, while H, I and J represent the same alloys extruded and heat treated for one hour at 425 C.

Table N 0. 2

Yield Tensile Elonga- Anoy :rx; 1 int sltgength tioa hBl'ldlillfll s. can ar ess M sq. sq. inches The effects of varying amounts of magnesium and manganese are illustrated by Table No. 3 which presents alloys in the extruded condition which have been heat treated for one hour at about 425 C. and quenched.

Table No.8

' Yield Tensile Elonga may .s it? as; as"

. can 9% mm all? sq. me...

x 10 1.0 33,305 69,450 27.2 09.4 L 12 1.0 MM 70,350 21.7 113.2 M 8.5 0.75 @555 59,775 26.5 89.3

Heat-treatment of aluminum-magnesium alloys containing manganese is especially advantageous where ductili is desired, but in some cases extreme ducti 'ty is obtained at the expense of a small decrease of tensile strength and hardness. For example, in Table N o. 2, alloy E as extruded has a tensile strength of 65,220 and an elon tion of 31.7; whereas for the same alloy esignated H) heated for one hour'at 425 C. and then quenched, the figures are 63,650 and 36.0 respectively, a loss of about 2 per cent in tensile strength and a gain of about 14 er cent in elongation. On the other hand, tween alloys F and I, containing 1.0 per cent of manganese, the heat-treatment increased the tensile strength about 13 per centand the elongation about 32 per cent.

Table No. 4 gives the physical properties found with 14 gauge sheet made from alloys containing 10 per cent of magnesium and no manganese, and -10 per cent of magnesium with 0.3 and 0.5 per cent of manganese. The values given were obtained with sheet which had been heat-treated for one-half hour at 425 C. and quenched in water.

i It will be seen that aluminum-magnesium alloys containing a substantial amount of magnesium and a small amount of manganese have physical properties equal to and in some cases exceeding those of any of the aluminum base alloys heretofore known and that this improvement is not confined to a single property. It isa feature of the invention that-the addition 'of a relatively small amount of manganese does not materiall lower any of the useful properties of the ahoy, while in some cases all are improved. In speaking of duc tility we are considering the property as indicated or measured by the conventional tests for elongation, that is to say, the percentage of elongation in two inches.

Another advanta e of our alloys is found in their improved forgeability or capability of being shaped by forging. This improvement 1s well shown by decreased tendency to cracking in the flash the cracking bemg m some cases entirely a sent.

It is to be understoo that the invention is not limited to the details specifically stated,

since these may vary without departure from the invention as efined by the following claims.

We claimin extruded mama num; the alloy having a tensile strength at least about 50,000

pounds per square inch and a Brinell hard ness of at least about 80.

2. An aluminum-"magnesium working aly consisting of magnesium about 10 per cent, manganese from about 0.2 to 1.5 per cent, and the rest aluminum; the alloy'havmg inextruded condition a tensile strength of at least about 60,000 pounds per s uare inch and a Brinell hardness of at least a out 90.

In testimony whereof we hereto afix our signatures.

ROBERT S. ARCHER.

LOUIS W. KEMPF. 

